MR-compatible implantable medical lead

ABSTRACT

A medical electrical lead may include a lead body having a proximal end and a distal end, a conductive electrode shaft located near the distal end within the lead body, a coiled conductor extending within the lead body from the proximal end and coupled to a first end of the conductive electrode shaft, and an electrode located near the distal end of the lead body and coupled to an opposite end of the conductive electrode shaft as the coiled conductor. The lead may also include an energy dissipating structure located near the distal end of the lead body and formed from a conductive material that defines a lumen through which a portion of the coiled conductor extends. The portion of the coiled conductor extending through the lumen defined by the energy dissipating structure is formed to provide an interference contact with the energy dissipating structure.

This application claims the benefit of U.S. Provisional Application No.61/717,462, filed on Oct. 23, 2012 and claims the benefit of U.S.Provisional Application No. 61/723,012, filed on Nov. 6, 2012. Theentire content of both of these applications is incorporated herein byreference in their entirety.

TECHNICAL FIELD

The present disclosure relates to MR-compatible implantable medicalleads.

BACKGROUND

In the medical field, implantable medical electrical leads are used witha wide variety of medical devices. For example, implantable medicalelectrical leads are commonly used to form part of an implantablemedical system that provides therapeutic electrical stimulation to apatient, such as cardiac electrical stimulation to the heart in the formof pacing, cardioversion, defibrillation, or resynchronization pulses.The pulses can be delivered to the heart or other desired locationwithin the patient via electrodes disposed on the leads, e.g., typicallynear distal ends of the leads. In that case, the leads may position theelectrodes with respect to various locations so that the implantablemedical system can deliver pulses to the appropriate locations. Leadsare also used for sensing purposes, or for both sensing and stimulationpurposes. Implantable leads are also used in neurological devices todeliver electrical stimulation to reduce the effects of a number ofneurological disorders and in a number of other contexts.

Patients that have implantable medical systems may benefit, or evenrequire, various medical imaging procedures to obtain images of internalstructures of the patient. One common medical imaging procedure ismagnetic resonance imaging (MRI). MRI procedures may generate higherresolution and/or better contrast images (particularly of soft tissues)than other medical imaging techniques. MRI procedures also generatethese images without delivering ionizing radiation to the body of thepatient, and, as a result, MRI procedures may be repeated withoutexposing the patient to such radiation.

During an MRI procedure, the patient or a particular part of thepatient's body is positioned within an MRI device. The MRI devicegenerates a variety of magnetic and electromagnetic fields to obtain theimages of the patient, including a static magnetic field, gradientmagnetic fields, and radio frequency (RF) fields. The static magneticfield may be generated by a primary magnet within the MRI device and maybe present prior to initiation of the MRI procedure. The gradientmagnetic fields may be generated by electromagnets of the MRI device andmay be present during the MRI procedure. The RF fields may be generatedby transmitting/receiving coils of the MRI device and may be presentduring the MRI procedure. If the patient undergoing the MRI procedurehas an implantable medical system, the various fields produced by theMRI device may have an effect on the operation of the medical leadsand/or the implantable medical device (IMD) to which the leads arecoupled. For example, the gradient magnetic fields or the RF fieldsgenerated during the MRI procedure may induce energy on the implantableleads (e.g., in the form of a current), which may be conducted to tissuevia the electrodes of the lead.

SUMMARY

An implantable medical lead may include components or mechanisms thatcan reduce the amount of induced current that is conducted to electrodesof the lead. This disclosure provides a medical lead(s) that include anenergy dissipating structure that provides a second path in parallelwith the electrical path from a coiled conductor to an electrode of thelead to redirect or shunt high frequency energy/signals away from theelectrode. This disclosure provides techniques for electrically couplingthe energy dissipating structure to the coiled conductor associated withthe electrode.

In one example, this disclosure is directed to a medical electrical leadincluding a lead body having a proximal end configured to couple to animplantable medical device and a distal end, a conductive electrodeshaft located near the distal end within the lead body, a coiledconductor extending within the lead body from the proximal end andcoupled to a first end of the conductive electrode shaft, an electrodelocated near the distal end of the lead body and coupled to an oppositeend of the conductive electrode shaft as the coiled conductor, and anenergy dissipating structure located near the distal end of the leadbody and formed from a conductive material that defines a lumen throughwhich a portion of the coiled conductor extends. The portion of thecoiled conductor extending through the lumen defined by the energydissipating structure is formed to provide an interference contact withthe energy dissipating structure.

In another example, this disclosure is directed to an implantablemedical system comprising an implantable medical device and animplantable medical electrical lead. The implantable medical electricallead includes a lead body having a proximal end configured to couple tothe implantable medical device and a distal end, a conductive electrodeshaft located near the distal end within the lead body, a coiledconductor extending within the lead body from the proximal end andcoupled to a first end of the conductive electrode shaft, an electrodelocated near the distal end of the lead body and coupled to an oppositeend of the conductive electrode shaft as the coiled conductor, and anenergy dissipating structure located near the distal end of the leadbody and formed from a conductive material that defines a lumen throughwhich a portion of the coiled conductor extends. The portion of thecoiled conductor extending through the lumen defined by the energydissipating structure is configured to provide an interference contactwith the energy dissipating structure that is substantially continuous.

In a further example, this disclosure is directed to a medicalelectrical lead including a lead body having a proximal end configuredto couple to an implantable medical device and a distal end, anelectrode located near the distal end of the lead body, a coiledconductor extending within the lead body from the proximal end andcoupled to the electrode, and an energy dissipating structure locatednear the distal end of the lead body and formed from a conductivematerial that defines a lumen through which a portion of the coiledconductor extends, wherein the portion of the coiled conductor extendingthrough the lumen defined by the energy dissipating structure is formedto provide an interference contact with the energy dissipating structurethat is substantially continuous.

The portion of the coiled conductor extending through the lumen definedby the energy dissipating structure may be formed to have one or moresections having windings of a first outer diameter and one or moresections having windings of a second outer diameter, wherein the secondouter diameter is greater than the first outer diameter and the sectionshaving windings of the second outer diameter provide the interferencecontact with the energy dissipating structure. In one example, the lumendefined by the conductive material of the energy dissipating structurehas an inner diameter and the second outer diameter of the sections ofthe coiled conductor may be approximately equal to the inner diameter ofthe lumen defined by the conductive material of the energy dissipatingstructure. In another example, the lumen defined by the conductivematerial of the energy dissipating structure has an inner diameter andthe second outer diameter of the sections of the coiled conductor may belarger than the inner diameter of the lumen defined by the conductivematerial of the energy dissipating structure.

The coiled conductor may have a pre-formed geometry such that theportion of the coiled conductor extending through the lumen defined bythe energy dissipating structure provides the interference contact withthe energy dissipating structure. The portion of the coiled conductorextending through the lumen defined by the energy dissipating structuremay be shaped into one of an arc and an undulated pattern. This may be aresult of the pre-formed geometry or shape of the coiled conductor. Theinterference contact between the energy dissipating structure and theportion of the coiled conductor extending through the lumen defined bythe energy dissipating structure may be substantially continuous duringmovement of the lead.

This summary is intended to provide an overview of the subject matterdescribed in this disclosure. It is not intended to provide an exclusiveor exhaustive explanation of the techniques as described in detailwithin the accompanying drawings and description below. Further detailsof one or more examples are set forth in the accompanying drawings andthe description below. Other features, objects, and advantages will beapparent from the description and drawings, and from the statementsprovided below.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram illustrating an environment in which apatient with an implantable medical system is exposed to externalfields.

FIG. 2 is a schematic diagram illustrating an example implantablemedical system.

FIG. 3 is a schematic diagram illustrating a longitudinalcross-sectional view of a distal end of a lead.

FIGS. 4A-4C illustrate various views of an example energy dissipatingstructure in further detail.

FIGS. 5A-5C illustrate another example of an energy dissipatingstructure.

FIG. 6 is a schematic diagram illustrating another example energydissipating structure.

FIGS. 7A and 7B are schematic diagrams illustrating various views of adistal end of another example lead.

FIG. 8 illustrates another example of a distal end of another examplelead.

FIG. 9 illustrates another example of a distal end of another examplelead.

FIG. 10 illustrates another example of a distal end of another examplelead.

FIG. 11 illustrates another example of a distal end of another examplelead.

FIG. 12 illustrates another example of a distal end of another examplelead.

DETAILED DESCRIPTION

FIG. 1 is a conceptual diagram illustrating an environment 10 in which apatient 12 with an implantable medical system 14 is exposed to externalfields 18. In the example illustrated in FIG. 1, environment 10 includesan MRI device 16 that generates external fields 18. MRI device 16generates magnetic and RF fields to produce images of body structuresfor diagnosing injuries, diseases and/or disorders. In particular, MRIdevice 16 generates a static magnetic field, gradient magnetic fieldsand RF fields as is well known in the art. The static magnetic field isa non time-varying magnetic field that is typically always presentaround MRI device 16 whether or not an MRI procedure is in progress.Gradient magnetic fields are pulsed magnetic fields that are typicallyonly present while the MRI procedure is in progress. RF fields arepulsed high frequency fields that are also typically only present whilethe MRI procedure is in progress.

The magnitude, frequency or other characteristic of the static magneticfield, gradient magnetic fields and RF fields may vary based on the typeof MRI device producing the field or the type of MRI procedure beingperformed. For example, a 1.5 Tesla (T) MRI device will produce a staticmagnetic field of about 1.5 T and have a corresponding RF frequency ofabout 64 megahertz (MHz) while a 3.0 T MRI device will produce a staticmagnetic field of about 3.0 T and have a corresponding RF frequency ofabout 128 MHz. However, other MRI devices may generate fields ofdifferent strengths and/or frequencies

Implantable medical system 14 may, in one example, include animplantable medical device (IMD) connected to one or more leads. The IMDmay be an implantable cardiac device that senses electrical activity ofa heart of patient 12 and/or provides electrical stimulation therapy tothe heart of patient 12. For example, the IMD may be an implantablepacemaker, implantable cardioverter defibrillator (ICD), cardiacresynchronization therapy defibrillator (CRT-D), cardioverter device, orcombinations thereof. The IMD may alternatively be a non-cardiacimplantable device, such as an implantable neurostimulator or otherdevice that provides electrical stimulation therapy.

Although environment 10 is described as including an MRI device 16 thatgenerates external fields 18, environment 10 may include other sourcesof external fields 18, such as devices used for electrocauteryprocedures, diathermy procedures, ablation procedures, electricaltherapy procedures, magnetic therapy procedures or the like. Moreover,environment 10 may include a non-medical source of external fields 18,such as an interrogation unit of a radio frequency (RF) security gate.

FIG. 2 is a schematic diagram illustrating an example implantablemedical system 20. Implantable medical system 20 may, for example,correspond with implantable medical system 14 of FIG. 1. Implantablemedical system 20 includes an IMD 22 and leads 24 a and 24 b (sometimesreferred to herein as leads 24 or leads 24 a,b). IMD 22 may be animplantable cardiac device that senses electrical activity of a heartand/or provides electrical stimulation therapy to the heart. IMD 22 may,for example, be an implantable pacemaker, implantable ICD, implantableCRT-D, implantable cardioverter device, or other device or combinationsthereof. IMD 22 may alternatively be a non-cardiac implantable device,such as an implantable neurostimulator or other device that provideselectrical stimulation therapy.

IMD 22 includes a housing 26 within which components of IMD 22 arehoused. Housing 26 can be formed from conductive materials,non-conductive materials or a combination thereof. IMD 22 includes apower source 28 and a printed circuit board (PCB) 30 enclosed withinhousing 26. Power source 28 may include a battery, e.g., a rechargeableor non-rechargeable battery, or other power source. PCB 30 includes oneor more electrical components (not shown in FIG. 2) of IMD 22, such asone or more processors, memories, transmitters, receivers, sensors,sensing circuitry, therapy circuitry and other appropriate components.

PCB 30 may provide electrical connections between power source 28 andthe electrical components of IMD 22 such that power source 28 powers thevarious electrical components of PCB 30. In some examples, PCB 30 mayinclude one or more layers of conductive traces and conductive vias thatprovide electrical connection between power source 28 and the electricalcomponents as well as provide electrical connections among the variouselectrical components. PCB 30 may not be limited to typical PCBstructures, but may instead represent any structure within IMD 22 thatis used to mechanically support and electrically connect the electricalcomponents of IMD 22 and power source 28. Moreover, although theelectronics components of IMD 22 are described as being on a single PCB,it is contemplated that the electronic components described herein maybe included elsewhere within IMD 22, e.g., on other supportingstructures within IMD 22, such as additional PCBs (not shown).

Leads 24 a,b each include a respective tip electrode 36 a,b and ringelectrode 38 a,b located near a distal end of respective leads 24 a,b.In other examples, however, leads 24 a,b may include more or fewerelectrodes. When implanted, tip electrodes 36 a,b and/or ring electrodes38 a,b are placed relative to or in a selected tissue, muscle, nerve orother location. In the example illustrated in FIG. 2, tip electrodes 36a,b are extendable helically shaped electrodes to facilitate fixation ofthe distal end of leads 24 a,b to the target location within patient 12.In this manner, tip electrodes 36 a,b are formed to define a fixationmechanism. In other embodiments, one or both of tip electrodes 36 a,bmay be formed to define fixation mechanisms of other structures. Inother instances, leads 24 a,b may include a fixation mechanism separatefrom tip electrode 36 a,b. In this case, tip electrodes 36 a,b may bepassive, such as a hemispherical electrode or ring electrode. Fixationmechanisms can be any appropriate type, including a grapple mechanism, ahelical or screw mechanism, a drug-coated connection mechanism in whichthe drug(s) serves to reduce infection and/or swelling of the tissue, orother attachment mechanism.

Leads 24 a,b are connected at a proximal end to IMD 22 via connectorblock 42. Connector block 42 may include one or more ports thatinterconnect with one or more connector terminals located on theproximal end of leads 24 a,b. Leads 24 a,b are ultimately electricallyconnected to one or more electrical components on PCB 30 through, forexample, connecting wires 44 that may extend within connector block 42.For example, connecting wires 44 may be connected to leads 24 a,b at oneend, and connected to PCB connection points 46 on PCB 30 at the otherend.

One or more conductors (not shown in FIG. 2) can extend within a body ofleads 24 a,b from connector block 42 to engage the ring electrode 38 a,band tip electrode 36 a,b, respectively. Each of the electricalconductors forms part of an electrical path from the proximal end ofleads 24 a,b to respective ones of electrodes 36 a,b or 38 a,b. The bodyof leads 24 a,b may be formed from a non-conductive material, includingsilicone, polyurethane, fluoropolymers, mixtures thereof, and otherappropriate materials, shaped to form a lumen within which the one ormore conductors extend. In this manner, each of tip electrodes 36 a,band ring electrodes 38 a,b is electrically coupled to a respectiveconductor within the lumen of the associated lead bodies. For example, afirst electrical conductor can extend along the length of body of lead24 a from connector block 42 and electrically couple to tip electrode 36a and a second electrical conductor can extend along the length of thebody of lead 24 a from connector block 42 and electrically couple toring electrode 38 a. The respective conductors may couple to circuitry,such as a therapy module or a sensing module, of IMD 22 via connectionsin connector block 42, connecting wires 44 and PCB connection points 46.The electrical conductors conduct therapy generated by the therapymodule within IMD 22 to combinations of electrodes 36 a,b and 38 a,b andtransmit sensed electrical signals from electrodes 36 a,b and 38 a,b tothe sensing module within IMD 22.

A patient having implanted medical system 20 may receive a certaintherapy or diagnostic technique, surgery, or other procedure thatexposes implantable medical system 20 to external fields, such asexternal fields 18 of FIG. 1. In the case of an MRI procedure, forexample, implantable medical system 20 is exposed to high frequency RFpulses and various magnetic fields to create image data regarding thepatient 12. The RF pulses can induce currents within the leads 24 a,b ofthe IMD 22, e.g., on the conductors of leads 24 a,b. The current inducedin the leads 24 a,b can cause certain effects, including heating, of thevarious lead components and/or tissue near the lead. According tovarious embodiments, such as those discussed herein, components ormechanisms can be provided to reduce or eliminate the amount of currentat tip electrodes 36 a,b and/or ring electrodes 38 a,b.

According to various embodiments discussed herein, one or both of leads24 a,b include components or mechanisms to reduce or eliminate theamount of current induced by external fields. To this end, each of leads24 a,b includes a respective energy dissipating structure 40 a,b thatfunctions as a shunt to redirect at least a portion of the currentinduced on leads 24 a,b is redirected. In one example, energydissipating structures 40 a,b are coupled to the conductors that formpart of the electrical path from the proximal end of leads 24 a,b to tipelectrodes 36 a,b. In this manner, energy dissipating structures 40 a,bprovide a second electrical path that is in parallel with the electricalpath through respective tip electrodes 36 a,b. Energy dissipatingstructures 40 a,b are designed to present low impedances at highfrequencies, such as those frequencies produced by MRI device 16,thereby redirecting a significant amount of current induced by the highfrequency signals from the first electrical paths through tip electrodes36 a,b to the second electrical paths through energy dissipatingstructures 40 a,b.

Redirecting or shunting at least a portion of the induced current fromtip electrodes 36 a,b to energy dissipating structures 40 a,b increasesthe area over which the current or thermal energy is dissipated, therebydecreasing the amount of heating adjacent to tip electrodes 36 a,b.Energy dissipating structures 40 a,b may, for example, comprise aconductive housing, a ring electrode, a sheath, a sleeve head, or anelectrically and thermally conductive material. In this manner, themedical electrical leads described in this disclosure may allow apatient to undergo medical procedures that utilize high frequencysignals without significantly affecting operation of the implantablemedical system.

The conductors, and particularly the conductor associated with tipelectrodes 36 a,b, may be a coiled conductors formed from one or morewire filars wound to form the coiled conductor. These coiled conductorshave inherent spring properties due to the fact that they are formed bywinding the one or more wire filars. The inherent spring properties ofthe coiled conductors may be used to achieve an interference contactbetween the coiled conductors and energy dissipating structure 40. Forexample, the inherent spring properties that are present in lead coiledconductors along with a geometry of either the energy dissipatingstructure 40, a distal sleeve head, and/or the coiled conductor itselfallow the coil to maintain contact with the energy dissipating structure40 or connection component coupled to the energy dissipating structure.

Energy dissipating structures 40 a,b may be coupled to the conductorsvia a number of different mechanisms described in this disclosure. Inone example, an inner geometry of a portion of energy dissipatingstructures 40 a,b may be formed to contact the conductors and force theportion of the conductors extending through energy dissipatingstructures 40 a,b off center. In other words, the geometry of the innersurface of energy dissipating structures 40 a,b may cause the conductorsextending through that portion to follow an undulated, sinusoidal, orhelical sweep path. In another example, the conductors may be coupled tothe energy dissipating structures 40 a,b by shifting the conductor axisnear a distal end of the lead off center via a lumen position changewithin the lead or within the distal sleeve heads. In a furtherembodiment, the conductors themselves may be modified in the vicinity ofthe energy dissipating structure 40 a,b to couple to the energydissipating structures 40 a,b. Each of these examples, which will bedescribed in more detail in the subsequent figures, provides aninterference contact using the inherent spring properties of the coiledconductors, thereby providing a consistent, low cost connection betweenthe conductor and the energy dissipating structures 40 a,b. Moreover, insome instances, the connection between the conductor and the energydissipating structures 40 a,b is made without relying on separateconnection components.

The embodiments described in this disclosure are generally discussed inthe context of reducing induced current to tip electrodes 36 a,b.However, this disclosure is not limited to such embodiments. One ofskill in the art would understand that modifications may be made toreduce the amount of induced current conducted to ring electrodes 38 a,bin addition to or instead of tip electrodes 36 a,b. As such, theconfiguration of implantable medical system 20 of FIG. 2 is merely anexample. Modifications may be made while still remaining within thescope of this disclosure.

The techniques of this disclosure may be used with leads have a coaxial,co-radial (or isodiametric), multi-lumen or other lead design. In someexamples, implantable medical system 20 may include more or fewer leadsextending from IMD 22. For example, IMD 22 may be coupled to threeleads, e.g., implanted within the right atrium, right ventricle and leftventricle of the heart. In another example, IMD 22 may be coupled to asingle lead that is implanted within either an atrium or ventricle ofthe heart. As such, implantable medical system 20 may be used for singlechamber or multi-chamber cardiac rhythm management therapy.

In addition to more or fewer leads, each of the leads 24 may includemore or fewer electrodes. In instances in which IMD 22 is used fortherapy other than pacing, e.g., defibrillation or cardioversion, theleads may include elongated electrodes, which may, in some instances,take the form of a coil. IMD 22 may deliver defibrillation orcardioversion shocks to the heart via any combination of the elongatedelectrodes and housing electrode. As another example, medical system 20may include leads with a plurality of ring electrodes, e.g., as used insome implantable neurostimulator, with a conductor associated with eachof the plurality of ring electrodes and having one or a plurality oflumens.

FIG. 3 is a schematic diagram illustrating a longitudinalcross-sectional view of a distal end of a lead 24. Lead 24 maycorrespond with lead 24 a or lead 24 b of FIG. 2. Lead 24 includes a tipelectrode 36 and possibly a ring electrode (not shown). Tip electrode 36may be electrically coupled to one or more electronic components on PCB30 of IMD 22 via an electrical path that exists from a proximal end oflead 24 (which is coupled to connector block 42 of IMD 22) to tipelectrode 36. In the example illustrated in FIG. 3, the electrical pathfrom the proximal end of lead 24 to tip electrode 36 includes a coiledconductor 52 and an electrode shaft 50.

In the example illustrated in FIG. 3, electrode shaft 50 is connected atone end to coiled conductor 52 and at the other end to tip electrode 36.Electrode shaft 50 may be connected to coiled conductor 52 and tipelectrode 36 via welding, soldering, crimping or other connectionmechanism. Coiled conductor 52, electrode shaft 50 and tip electrode 36may all be formed at least partially from a conductive material, such astitanium, titanium alloy, tantalum, tantalum alloy platinum, platinumiridium, conductive polymers, and/or other suitably conductive materialor combination of materials. Coiled conductor 52, electrode shaft 50 andtip electrode 36 may be all formed of the same conductive material ordifferent conductive materials. In one example, coiled conductor 52 is amulti-filar coil having a plurality of co-radially wound wire filars.

The mechanical coupling of coiled conductor 52, electrode shaft 50 andtip electrode 36 provides a mechanical relationship that may, in someinstances, allow for mechanical control of tip electrode 36 such that itmay be extended from and retracted within the distal end of lead 24.During implantation, for example, a physician or other user may interactwith lead 24 to rotate coiled conductor 52, which causes electrode shaft50 to rotate and extend/retract tip electrode 36 from the distal end oflead 24. In this manner, tip electrode 36 may be screwed into the targettissue location. As such, coiled conductor 52 may have sufficientrigidity to assist in attaching tip electrode 36 to the target tissuelocation while being flexible enough to navigate through body lumens,e.g., through one or more veins. In other examples, tip electrode 36 maybe extended/retracted via a translational force instead of a rotationalforce. In other instances, electrode shaft 50 may be formed to receive astylet to guide lead 24 during implantation or to allow a user to extendand/or retract tip electrode 36. In further instances, lead 24 may notinclude an electrode shaft 50. Instead, conductor 52 may be directlyconnected to tip electrode 36 and may or may not allow for mechanicalcontrol of tip electrode 36

As described above, certain therapy or diagnostic techniques, such as anMRI procedure, may expose lead 24 to high frequency RF pulses andmagnetic fields. Additionally, certain non-medical environments may alsoinclude RF fields to which lead 24 is exposed. The RF pulses can inducecurrents on conductor 52 within lead 24 of the IMD 22. The inducedcurrent on conductor 52 may be conducted to tip electrode 36. Lead 24includes components or mechanisms that can reduce the amount of inducedcurrent that is conducted to tip electrode 36. Although described in thecontext of reducing current to tip electrode 36, lead 24 may includesimilar mechanism or other mechanisms that may reduce the inducedcurrent conducted to ring electrodes in addition to tip electrodes 36.

Lead 24 of FIG. 3 includes an energy dissipating structure 40 that iselectrically coupled to the electrical path from the proximal end oflead 24 to tip electrode 36 near the distal end of lead 24. Inparticular, energy dissipating structure 40 is electrically coupled tocoiled conductor 52 near the distal end of lead 24 to provide a secondelectrical path through energy dissipating structure 40 that is inparallel with the electrical path through tip electrode 36.

Energy dissipating structure 40 presents a high impedance at lowfrequencies, such as those frequencies used for pacing or otherstimulation therapies (e.g., ˜1 kHz for pacing signals). As such, only asmall amount of current is redirected away from tip electrode 36, e.g.,along the second electrical path to energy dissipating structure 40, atlow frequencies. In this manner, energy dissipating structure 40functions as a shunt for high frequency energy by essentially havingelectrical isolation at low pacing frequencies allowing pacing to occurat the tip electrode surface. Energy dissipating structure 40 presents alow impedance at high frequencies, such as those frequencies produced byMRI device 16 (greater than 1.0 MHz), resulting in a significant amountof the induced current being redirected away from the first electricalpath through tip electrode 36 to the second electrical path throughenergy dissipating structure 40. Thus, energy dissipating structure 40functions by coupling a significant amount of the higher frequencyenergy through the energy dissipating structure 40. In one example, anelectrical lead with an energy dissipating structure 40 as describedherein may result in at least 50% of the energy induced by highfrequency RF signals of an MRI device to be redirected away from tipelectrode 36 while less than 10% of the energy associated with a pacingtherapy is directed through energy dissipating structure 40.

In some instances, energy dissipating structure 40 has a surface areathat is significantly larger than a surface area of tip electrode 36.The surface area of energy dissipating structure 40 may, in one example,be between approximately 20-100 mm², which is at least approximately tentimes larger than the surface area of tip electrode 36. A large surfacearea ratio, defined by the ratio of the surface area of energydissipating structure 40 to the surface area of tip electrode 36 isdesired to dissipate the induced current over a larger area to reduceheating at any specific location.

Energy dissipating structure 40 may include a conductive material thatis at least partially covered by a layer of insulating material. In oneexample, the insulation material may cover at least the portion ofenergy dissipating structure 40 that is exposed to the bodily fluidand/or tissue of patient 12 such that the outer surface of theconductive material of energy dissipating structure 40 does not contacta body of the patient when implanted. In other instances, however,conductive material of energy dissipating structure 40 may be directlyexposed to bodily fluid and/or tissue, i.e., not include the layer ofinsulating material. Conductive material may be an electrically andthermally conductive material, such as titanium, titanium alloy,tantalum, tantalum alloy, platinum, platinum iridium, conductivepolymers, nickel-cobalt alloy (e.g., MP35N®) and/or other suitablyconductive material or combination of materials.

The insulating material may cover an outer surface of conductivematerial or at least a portion of the outer surface of conductivematerial. Insulating material may affect the impedance of energydissipating structure 40 and reduce the effect of energy dissipatingstructure 40 on the tip electrode to tissue interface impedances. As thethickness of insulating material increases, the capacitance associatedwith energy dissipating structure 40 decreases and the impedance ofenergy dissipating structure 40 increases. As a result the amount ofcurrent redirected to energy dissipating structure 40 is reduced, butthere is less interference with therapy delivered by IMD 22. As thethickness of insulating material 64 decreases, the capacitanceassociated with energy dissipating structure 40 increases and theimpedance of energy dissipating structure 40 decreases. As a result theamount of current (even at low frequencies) redirected to energydissipating structure 40 is increased, which may affect therapydelivered IMD 22.

For example, an energy dissipating structure 40 having a surface area ofapproximately 22 square millimeters (mm²) and an insulating materialhaving a dielectric constant of approximately 4.0, an insulatingmaterial thickness of approximately 68 micrometers provides an impedanceof approximately 10 Ohms and a capacitance of approximately 250 pF, athickness of approximately 34 micrometers provides an impedance ofapproximately 5 Ohms and a capacitance of approximately 500 pF, and athickness of approximately 17 micrometers provides an impedance ofapproximately 2.5 Ohms and a capacitance of approximately 1 nF. Thesevalues are only exemplary in nature. The electrical characteristics ofenergy dissipating structure 40 may take on different values dependingon the construction of the distal end of lead 24, e.g., based on thesurface area of tip electrode 36, the surface area of energy dissipatingstructure 40, the thickness of insulating material, the material fromwhich the various components are constructed, and the like.

The thickness of insulating material may be selected by a therapysystem/lead designer to achieve a satisfactory tradeoff betweencapacitance and impedance. Numerous techniques may be employed tointroduce insulating material over the outside of energy dissipatingstructure 40 and/or partially inside energy dissipating structure 40.Exemplary techniques include anodizing, chemical vapor deposition, diplayer, spraying, thermal reflow, or thermal extrusion or molding.

Insulating material may also cover at least a portion of an innersurface of conductive material. Insulating material on the inner surfacemay prevent conductive material of energy dissipating structure 40 frommaking direct contact with the conductive material of tip electrode 36,electrode shaft 50 and/or coiled conductor 52 at locations other thandesired. In some instances, the insulating material may even cover thesurface of the portion of conductive material contacting coiledconductor 52. In this case, the coupling between energy dissipatingstructure 40 and coiled conductor 52 is a non-conductive (e.g.,capacitive or thermal) coupling instead of a conductive coupling. Insome instances, energy dissipating structure 40 may include more thanone layer of insulating material, with each layer being made of the sameor different insulating material. Insulating material may includeparylene, metal oxides, polyimide, urethane, silicone,tetrafluroethylene (ETFE), polytetrafluroethylene (PTFE), polyetherether ketone (PEEK), oxides, or other suitable non-conductive materialor combination of materials.

It is desirable that the contact between energy dissipating structure 40and coiled conductor 52 is continuous, as intermittent metal-metalcontact of coiled conductor 52 and energy dissipating structure 40 maygenerate electrical noise. Moreover, with extendable\retractable leadsthis electrical connection/contact, the tip electrode 36 (which may be ahelix as illustrated in FIG. 3) and inner circuit (which may includecoiled conductor 52 and electrode shaft 50) may rotate while the energydissipating structure 40 remains fixed. It is thus desirable to have anelectrical connection/contact that reduces the effect on lead extensionperformance while maintaining constant contact and presents a lowresistance connection during MRI procedures. It may also be desirable tohave the connection/contact mitigate electrical noise that could begenerated via by intermittent metal-metal contact of inner circuit andenergy dissipating structure 40 or by this electrical connection. Noisegenerated by intermittent contact could present itself as cardiacsignals since the lead tip is moving at the same rate as the heart insome cardiac implementations. To help mitigate this noise potential theenergy dissipating structure 40 can be completely isolated with theexception of this electrical connection and/or this electricalconnection need to be of low enough resistance to drain off/ground themetal components resting potential such that noise is minimized by metalto metal contact.

Past solutions have been to make springs, spring clips, conductiveseals, or the like that will make these electrical connections. Theseoptions require that separate component(s) be added that makes contactwith electrode shaft 50. Some of these solutions may utilize componentsthat are constructed of a material that is harder than that of electrodeshaft 50 (which may be constructed of materials such as platinum/iridium(Pt/Ir)) so that the electrical connection component will not easilyplastically deform and will maintain spring properties during assemblyand use. The softer material of electrode shaft 50 may, in someinstances, be subject to galling when used in combination with harderspring materials. Additionally, the smaller sizes and tolerances of thesprings, spring clips, conductive seals, or the like, make thesecomponents difficult and/or expensive to manufacture.

In accordance with one aspect of this disclosure, lead 24 may be formedto make electrical connection directly between coiled conductor 52 andenergy dissipating structure 40 by way of an interference contact. Inthe example of FIG. 3, the inherent spring properties that are presentin lead coils, such as coiled conductor 52, along with a geometry ofenergy dissipating structure 40 allow the coiled conductor 52 tomaintain constant electrical contact with energy dissipating structure40 and provide a consistent, low cost electrical connection directlybetween the coiled conductor 52 and the energy dissipating structure 40.

In the example illustrated in FIG. 3, the conductive material of energydissipating structure 40 defines a lumen through which a portion ofcoiled conductor 52 extends. Energy dissipating structure includes aregion having a plurality of protrusions 60 extending from an innersurface toward a central axis of the lumen defined by energy dissipatingstructure 40. Protrusions 60 contact portions of coiled conductor 52that extend through that portion of the energy dissipating structure 40to slightly force coiled conductor 62 off center in multiple locationsrelative to a central axis of the lumen formed by the energy dissipatingstructure. In this manner, protrusions 60 push portions of the coiledconductor 52 off center relative to the central axis such that coiledconductor follows a slightly undulated, sinusoidal, or helical sweeppath through the portion of energy dissipating structure 40 having theplurality of protrusions 60.

The natural response of coiled conductor 52, which has many inherentproperties similar to a spring, is to realign such that the coiledconductor 52 is no longer off center thus exerting a force againstprotrusions 60. The force provides an electrical connection achieved bythe friction between the coiled conductor 52 and energy dissipatingstructure 40. In this manner, the interference contact is accomplishedusing the inherent spring properties of coiled conductor 52 and thegeometry (formed by protrusions 60) of the inner surface of energydissipating structure 40.

The spacing between subsequent protrusions 60 along the length of energydissipating structure 60 may affect the extension/retractioncapabilities of lead 24. It may be desirable to space protrusions 60 (orsets of protrusions 60) along the longitudinal length of energydissipating structure 40 such that none of protrusions 60 contactsubstantially opposite sides of coiled conductor 52 within one andone-half (1½) turns of coiled conductor 52. Such spacing may be ofparticular interest in active fixation leads in which rotation of thecoiled conductor 52, electrode shaft 50, and/or tip electrode 36relative to the rest of the lead 24 is desirable. In fact, depending onthe desired handling and extension/retraction characteristics, thespacing of protrusions may be larger, e.g., such that none ofprotrusions 60 contact substantially opposite sides of coiled conductor52 within two or more turns of coiled conductor 52. The spacing betweenprotrusions 60 (or sets of protrusions 60) along the longitudinal lengthof energy dissipating structure 40 may also be less than that describedabove in some instances. In the case of passive fixation leads, in whichrotation of the coiled conductor 52, electrode shaft 50, and/or tipelectrode 36 relative to the rest of the lead 24 is not necessary, asmaller spacing between protrusions along the longitudinal length ofenergy dissipating structure 40 of less than one and one-half turns maybe used.

Additionally, the size and depth of protrusions 60 may affect theresistance of energy dissipating structure 60, affect how much coiledconductor 52 is off center and thereby how much force is exerted bycoiled conductor 52 on protrusions 60, affect the extension/retractioncapabilities of lead 24, and the like. As such, the size and depth ofprotrusions 60 may be formed such that force exerted against protrusions60 are sufficient to maintain contact with energy dissipating structure40 during flexing and other movement of lead 24, but still allow coiledconductor 52 to rotate and turn and allow a stylet to pass withoutsignificant interference of the stylet.

In the case of an active fixation lead, it may be desirable thatprotrusions 60 do not push coiled conductor 52 so far off center that itcontacts the portion of energy dissipating structure 40 substantiallyopposite of protrusions 60. In the example illustrated in FIG. 3, atleast some space still exists between coiled conductor 52 and theportion of energy dissipating structure 40 substantially oppositeprotrusions 60. In other instances (such as passive fixation leads andpossibly active fixation lead), some contact may occur, but the contactcannot interfere with the rotation of coiled conductor 52 and tipelectrodes 36.

In the example illustrated in FIG. 3, protrusions 60 are hemisphericalbumps that extend inward from the inner surface of energy dissipatingstructure 40. However, in other example, protrusions 60 may be made indifferent shapes including rectangular notches, square notches, ovalnotches, and the like. Protrusions 60 may be generated by crimping,staking, machining, molding, forming or other technique.

Lead 24 may also include a seal 56. Seal 56 may be in contact withenergy dissipating structure 40 and electrode shaft 50 to obstruct fluidfrom passing into the lumen defined by the body of the lead. Seal 56 maybe substantially ring (e.g. o-ring) or disk shaped but other suitableshapes may also be employed. In one example, seal 56 may be anon-conductive sealing washer or a conductive sealing washer with anon-conductive coating. Lead 24 may also include one more rings that mayhold seal 56 in place. In some instances, energy dissipating structure40 and/or electrode shaft 50 may also be in contact with rings. Ringsmay, in one example, be shaped as a non-conductive C-ring to receiveseal. However, rings of other shapes may be used. In further instances,lead 24 may not include any rings or seal 56.

FIGS. 4A-4C illustrates various views of energy dissipating structure 40of FIG. 3 in further detail. FIG. 4A illustrates a longitudinalcross-sectional view of energy dissipating structure 40. FIG. 4Billustrates a section view of energy dissipating structure 40 from A-A′.FIG. 4C is an angled view of energy dissipating structure 40.

Energy dissipating structure 40 defines a lumen 66 through which, asillustrated in FIG. 3, a portion of coiled conductor 52 extends. Energydissipating structure 40 includes a region having a plurality ofprotrusions 60 extending toward a central axis 68 of lumen 66 defined byenergy dissipating structure 40. As illustrated in FIG. 4A, pairs ofprotrusions 60 are separated from one another along a longitudinallength of the inner surface of energy dissipating structure 40. In theillustrated example, protrusions 60 are located at three cross-sectionallocations along the longitudinal length of energy dissipating structure40 (best illustrated in FIG. 4A). In other instances, however,protrusions may be located at more or less than three cross-sectionallocations along the longitudinal length of energy dissipating structure40.

Energy dissipating structure 40 further includes more than oneprotrusion 60 along the circumference of the inner surface of the energydissipating structure 40 at each of the cross-sectional locations. Inthe example illustrated in FIGS. 4A and 4B, for example, energydissipating structure 40 has a first set (or pair) of protrusions 60 at0 degree and 90 degree positions in the x-z plane at the firstcross-sectional location, a second set (or pair) of protrusions 60 at180 degree and 270 degree positions in the x-z plane at the secondcross-sectional location, and a third set (or pair) at the 0 degree and90 degree positions in the x-z plane at the third cross-sectionallocation. FIG. 4B illustrates the cross sectional view from A-A′, whichincludes the first set (or pair) of protrusions 60 that are located atapproximately the 0 degree and 90 degree positions in the x-z plane. Inother examples, energy dissipating structure 40 may include only asingle protrusion 60 at each of the cross-sectional locations or theprotrusions may be separated by varying degrees (e.g., greater than orless than 90 degrees).

As described above with respect to FIG. 3, protrusions 60 contactportions of coiled conductor 52 that extend along that portion of theenergy dissipating structure 40 to slightly force coiled conductor 62off center in multiple locations relative to a central axis of the lumendefined by energy dissipating structure 40. In this manner, protrusions60 push portions of the coil off center relative to the central axissuch that coiled conductor follows a slightly undulated, sinusoidal, orhelical sweep path through the portion of energy dissipating structure40 having the plurality of protrusions 60. In the example of FIGS. 4Aand 4B, the first pair of protrusions 60 in the first cross-sectionallocation push coiled conductor 52 downward and into of the page (e.g.,along the x- and z-axis), the second pair of protrusions 60 in thesecond cross-sectional location push coiled conductor 52 upward and outof the page (e.g., in approximately the opposite direction along the x-and z-axis), and the third pair of protrusions 60 in the thirdcross-sectional location push coiled conductor 52 upward and out of thepage (e.g., along approximately the same x- and z-axis as the first pairof protrusions).

The result is that coiled conductor 52 extends along a slightlysinusoidal, undulated or helical sweep path. The inherent springproperties of coiled conductor 52 exert a force against protrusions 60to achieve an interference connection between the coiled conductor 52and energy dissipating structure 40. In this manner, the interferencecontact or connection is accomplished using the inherent springproperties of coiled conductor 52 and the geometry (formed byprotrusions 60) of the inner surface of energy dissipating structure 40.Protrusions are formed such that the force exerted against protrusions60 are sufficient to maintain contact with energy dissipating structure40 during flexing and other movement of lead 24, but still allow coiledconductor 52 to rotate and turn and allow a stylet to pass withoutsignificant interference of the stylet.

Each of protrusions 60 contact one or more of the filars of coiledconductor 52. The number of protrusions 60, dimensions of protrusions60, and spacing between protrusions 60 along both the length and innercircumference may be designed to provide adequate contact with coiledconductor 52 without significantly affecting the extension andretraction capability of coiled conductor 52. For example, thelongitudinal length of protrusions 60 may be formed to come into contactwith multiple filars of coiled conductor 52. This, in effect, providesincreased contact points at each interface between energy dissipatingstructure 40 and coiled conductor 52 since each of the filars of coiledconductor 50 is independent. Additionally, the length of individualprotrusions 60 may be formed to prevent protrusions 60 from pushing,extending or otherwise dropping between filars of coiled conductor 52.For example, the length of protrusions 60 may be greater than thediameter of a single filar of the multi-filar lead. The length ofprotrusions 60 may, for example, be approximately equal two times, threetimes, or four times the diameter of a single filar. As such, each ofprotrusions 60 makes contact with more than one filar of a multi-filarconductor. For a multi-filar coil having a wire size of 0.005 diameter,protrusions 60 may have a length of approximately 0.010. In someinstances, protrusions 60 may be spaced to contact different ones of thefilars of coiled conductor 52. In this manner, protrusions 60 may bridgethe filars of coiled conductor 52 for a smoother extension/retraction.

The depth of protrusions 60, e.g., the distance from the inner surfaceof energy dissipating structure 40 to the portion of protrusions 60located closest to the central axis of the lumen defined by energydissipating structure 40, may also be designed to achieve particularcharacteristics. In the case of an active fixation lead, for example, itmay be desirable that the protrusions do not push coiled conductor 52 sofar off center that it contacts the portion of energy dissipatingstructure 40 opposite of protrusions 60. In other instances (such aspassive fixation leads and possibly active fixation lead), some contactmay occur between coiled conductor 52 and non-protrusion portions ofenergy dissipating structure 40, but the contact should not interferewith the rotation of coiled conductor 52, electrode shaft 50, and/or tipelectrodes 36. In other words, it is undesirable to have protrusions 60that are thick or deep enough to pinch, crush, or otherwise exert toomuch force on coiled conductor 52 such that extension and retraction oftip electrode 36 is affected.

Additionally, protrusions 60 (or sets of protrusions 60) may be spacedapart from one another along the longitudinal length of energydissipating structure 40 such that contact from subsequent protrusionsdoes not inhibit the extension/retraction capabilities. In the exampleconstruction illustrated in FIGS. 3 and 4 in which subsequent sets ofprotrusions 60 are located in locations substantially opposite from theprevious set of protrusions 60 (e.g., the first set (or pair) ofprotrusions 60 located 0 degree and 90 degree positions in the x-z planeat the first cross-sectional location and the second set (or pair) ofprotrusions 60 at 180 degree and 270 degree positions in the x-z planeat the second cross-sectional location), it may be desirable to spacesets of protrusions 60 along the longitudinal length of energydissipating structure 40 by at least one and one-half (1½) turns ofcoiled conductor 52. In this manner, coiled conductor 52 has traveled atleast one and one-half turns before any protrusions contact the filarsof coiled conductor 52 on substantially opposite sides of coiledconductor 52. In other words, it may be desirable that no subsequentprotrusions contact the opposite side of coiled conductor as a previousprotrusion until the coiled conductor 52 has extended at least one andone-half turns.

Such spacing may be of particular interest in active fixation leads inwhich rotation of the coiled conductor 52, electrode shaft 50, and/ortip electrode 36 relative to the rest of the lead 24 is desirable. Infact, depending on the desired handling and extension/retractioncharacteristics, the spacing of protrusions may be larger, e.g., suchthat none of protrusions 60 contact substantially opposite sides ofcoiled conductor 52 within two or more turns of coiled conductor 52. Thespacing between protrusions 60 (or sets of protrusions 60) along thelongitudinal length of energy dissipating structure 40 may also be lessthan that described above in some instances. In the case of passivefixation leads, in which rotation of the coiled conductor 52, electrodeshaft 50, and/or tip electrode 36 relative to the rest of the lead 24 isnot necessary, a smaller spacing between protrusions along thelongitudinal length of energy dissipating structure 40 of less than oneand one-half turns may be used.

The example illustrated in FIGS. 4A-4C illustrates one exampleconfiguration of energy dissipating structure 40. As described above,however, energy dissipating structure 40 may be designed to include moreor fewer protrusions having different shapes and being located indifferent locations without departing from the scope of this disclosure.For example, energy dissipating structure 40 may include protrusionslocated at three cross-sectional locations along the longitudinal lengthwith only one protrusion at each of the cross-sectional locations. Inthis alternate example, the protrusions may push the coil in oppositedirections at each subsequent cross-sectional location such that coiledconductor 52 follows a sinusoidal or undulated path or the protrusionsmay be arranged to be 90 degrees relative to one another (or some otherangle relative to one another) such that coiled conductor 52 followssome sort of helical sweep path.

FIG. 4C illustrates an angled view of energy dissipating structure 40.Energy dissipating structure 40 may have at least two sections thathaving different outer diameters. For example, a first section 62 ofenergy dissipating structure 40 has an outer diameter that isapproximately equal to the outer diameter of lead 24 such that it isexposed to the body of patient 12 and a second section 64 of energydissipating structure 40 has an outer diameter that is less than theouter diameter of lead 24.

In the example illustrated in FIG. 4C, first section 62 has a generallycylindrical shape and second section 64 has more of a rectangular shape.Such a construction may provide additional stability of first section 62when protrusions 60 are being formed via crimping, pressing, staking, orother similar technique. In other instances, the protrusions may beformed via machining or forming of energy dissipating structure. Inthese instances, the use of a generally cylindrical geometry may besufficient.

In some instances a kerf, groove or notch may be formed (e.g., via laseror other mechanism) in the region of energy dissipating structure 40including protrusions 60. The kerf, groove or notch would allow thatregion of energy dissipating structure 40 to bend or flex slightlyallowing for more intimate contact when the lead moves. The kerf, grooveor notch may be formed on an outer surface of the region of energydissipating structure 40 including protrusions 60. In one example, thekerf, groove or notch may be formed helically along the portion ofenergy dissipating structure 40 including protrusions 60. In otherinstances, the kerf, groove, or notch may take other shapes andarrangements, such as a plurality of kerfs, grooves or notches extendingaround the outer circumference of energy dissipating structure 40 andspaced apart from one another along the longitudinal length of theregion of energy dissipating structure 40 having protrusions 60.

FIGS. 5A-5C illustrate another example of an energy dissipatingstructure 40′ having protrusions 60′ of a different shape. Energydissipating structure 40′ of FIGS. 5A-5C conforms substantially toenergy dissipating structure 40 of FIGS. 4A-4C except protrusions 60′have a different shape. Energy dissipating structure 40′ may, forexample, replace energy dissipating structure 40 in the example leadconfiguration of FIG. 3.

In the example illustrated in FIGS. 5A-5C, protrusions 60′ are elongatedtrapezoidal shaped. Such a shape provides a larger surface area thatcontact with the filars of coiled conductor 52 than the hemisphericalbumps of FIGS. 3 and 4. The elongated trapezoidal shaped protrusions ofenergy dissipating structure 40′ may have a longitudinal length formedto come into contact with multiple filars of coiled conductor 52. This,in effect, provides increased contact points at each interface betweenenergy dissipating structure 40 and coiled conductor 52 since each ofthe filars of coiled conductor 50 is independent. The elongatedtrapezoidal shape may also have an arc-shaped innermost surface as thetrapezoidal shape extends partially around a portion of thecircumference of the energy dissipating structure 40′. Additionally, theelongated trapezoidal shape may have a reduced likelihood of protrusions60 pushing, extending or otherwise dropping between filars of coiledconductor 52 or between the windings of coiled conductor 52 (e.g.,within the space associated with the pitch of the windings of coiledconductor 52). The depth and spacing of protrusions 60 of FIGS. 5A and5B may be similar to that described above with respect to FIG. 4.

FIG. 5C illustrates an angled view of energy dissipating structure 40′.Energy dissipating structure 40′ has at least two sections that havingdifferent outer diameters, but unlike energy dissipating structure 40 ofFIG. 4C, both the first and second sections have a generally cylindricalshape.

FIG. 6 is a schematic diagram illustrating another example energydissipating structure 40″ that may be used within a distal end of alead, such as lead 24 of FIG. 3, in place of energy dissipatingstructure 40. Energy dissipating structure 40″ includes a protrusionthat forms an interference thread 68 (also referred to herein as ahelical sweep 68). In one example, interference thread or helical sweep68 may be an integral part of energy dissipating structure 40″, e.g.,formed via machining of inner surface of energy dissipating structure40″ to form interference thread or helical sweep 68, molding energydissipating structure 40″ to include interference thread or helicalsweep 68, rolling the pattern of interference thread or helical sweep 68into the tubular wall of energy dissipating structure 40″, or othertechnique. In another example, interference thread or helical sweep 68may be formed by introducing a separate component inserted into thelumen defined by energy dissipating structure 40″. The separatecomponent may be an elongated flat wire coil, a helical thread insert,or the like. The separate component may be made from the same materialas energy dissipating structure 40″ or a different material than energydissipating structure 40″

In either case, interference thread or helical sweep 68 interferes withcoiled conductor 52 to alter the path of coiled conductor 52 resultingin an interference contact with coiled conductor 52 and energydissipating structure 40″. Interference thread or helical sweep 68 maybe designed with a different pitch compared to a pitch of coiledconductor 52. For example, interference thread or helical sweep 68 mayhave an elongated pitch compared to the pitch of coiled conductor 52.Interference thread or helical sweep 68 may also be arranged in theopposite direction as the windings of coiled conductor 52. Havinginterference thread or helical sweep 68 have a different pitch thanand/or opposite direction of the windings of coiled conductor 52provides an interference contact with coiled conductor 52 that slightlyforces coiled conductor 62 off center relative to the central axis. Inother words, interference thread or helical sweep 68 pushes a portion ofthe coil off center relative to the central axis such that coiledconductor follows a slightly undulated, sinusoidal, or helical sweeppath through the portion of energy dissipating structure 40 having theinterference thread or helical sweep 68. This provides a continuous,constant electrical connection between energy dissipating structure 40and coiled conductor 52.

The pitch, direction, thickness, depth or other aspect of interferencethread or helical sweep 68 may be designed to provide adequate contactwith coiled conductor 52 without significantly affecting the extensionand retraction capability of coiled conductor 52. For example, pitch anddirection of interference thread or helical sweep 68 may be formed toprevent interference thread or helical sweep 68 from extending orotherwise falling between filars or between windings of coiled conductor52, which may interfere with extension and retraction, particularly whenthe direction of interference thread or helical sweep 68 is oppositethat of coiled conductor 52. In one example, the pitch of interferencethread or helical sweep 68 may be at least four times the pitch ofcoiled conductor 52. In this manner, coiled conductor 52 has traveled atleast one and one-half turns before any portions of helical sweep 68contact coiled conductor 52 on substantially opposite sides of coiledconductor 52. In other words, coiled conductor 52 has traveled at leastone and one-half turns before any portions of helical sweep 68 contactcoiled conductor 52 at a location approximately 180 degrees from anyprevious contact point of coiled conductor 52 and helical sweep 68.

In some instances, interference thread or helical sweep 68 (orarrangement of other protrusions 60 such as those in FIGS. 4 and 5) maywrap in the same direction as windings of coiled conductor 52 and mayalso have essentially the same pitch as windings of coiled conductor 52.In this manner, interference thread or helical sweep 68 (or otherprotrusions 60) may function as a tooth or guide that actually aids inthe extension/retraction of tip electrode 36.

In another example, the effect of helical sweep 68 on coiled conductor52 may be achieved by using a series of protrusions 60, e.g., bumps,elongated trapezoids or other shaped protrusions, which are locatedalong a path similar to helical sweep 68. In other words, theprotrusions are spaced along the longitudinal length and around thecircumference of energy dissipating structure 40 to achieve a similareffect of helical sweep 68.

Additionally, the energy dissipating structure illustrated in FIG. 6 mayinclude the one or more kerfs, grooves, or notches to allow that regionof energy dissipating structure 40 to bend or flex slightly allowing formore intimate contact when the lead moves, as described above withrespect to FIG. 4.

FIGS. 7A and 7B are schematic diagrams illustrating various views of adistal end of another example lead 70. Lead 70 may correspond with lead24 a or lead 24 b of FIG. 2. Lead 70 includes a tip electrode 36, ringelectrode 38, and a defibrillation electrode(s) 72. Each of tipelectrode 36, ring electrode 38, and defibrillation electrode 72 iselectrically coupled to one or more electronic components on PCB 30 ofIMD 22. As such, separate electrical paths exist from a proximal end oflead 70 (which is coupled to connector block 42 of IMD 22) to respectiveones of tip electrode 36, ring electrode 38, and defibrillationelectrode 72.

FIG. 7A illustrates a longitudinal cross-sectional view of the distalend of lead 70 and FIG. 7B illustrates a section view of the distal endof lead 70 from A-A′. As illustrated in FIG. 7B, lead 70 includesmulti-lumen lead body 74, which includes four lumens 76A-76D throughwhich each of the four conductors of lead 70 extend. Lead body 74 istypically comprised of extruded silicone rubber or other non-conductive,biocompatible material. Lead body 74 may be covered by sheathing 78 thatprotects the components of lead 70 from the environment of the body inwhich it is implanted. Sheathing 78 may be comprised of a polyurethaneor other non-conductive, bio-compatible material.

Conductors 80, 82 and 84 are illustrated in FIG. 7B as being strandedcable conductors in which a plurality of wire filars are wrapped aroundcentral wire filar inside sheathing 86. Conductors 80, 82, and 84 areconnected to respective electrodes. In the example of FIG. 7B, conductor80 is connected to ring electrode 38 (as illustrated in FIG. 7A).Although not illustrated in FIG. 7, conductors 82 and 84 are connectedto respective defibrillation electrodes 72. Conductor 80 is connected toring electrode 38. Although illustrated as stranded cable conductors,one or more of conductors 80, 82, and 84 may be other types ofconductors, such as modified stranded cable conductors (e.g., having anon-conductive core), coiled conductors, or the like.

The electrical path from the proximal end of lead 70 to tip electrode 36includes a coiled conductor 52 and an electrode shaft 50 similar to lead24 illustrated in FIG. 3. Electrode shaft 50 is connected at one end tocoiled conductor 52 and at the other end to tip electrode 36. Coiledconductor 52, electrode shaft 50 and tip electrode 36 may all be formedat least partially from a conductive material, such as titanium,titanium alloy, tantalum, tantalum alloy, platinum, platinum iridium,conductive polymers, and/or other suitably conductive material orcombination of materials. Coiled conductor 52, electrode shaft 50 andtip electrode 36 may be all formed of the same conductive material ordifferent conductive materials. In one example, coiled conductor 52 is amulti-filar coil having a plurality of co-radially wound bare wirefilars within a sheathing 86.

The mechanical coupling of coiled conductor 52, electrode shaft 50 andtip electrode 36 provides a mechanical relationship that may, in someinstances, allow for mechanical control of tip electrode 36 such that itmay be extended from and retracted within the distal end of lead 70.During implantation, for example, a physician or other user may interactwith lead 70 to rotate coiled conductor 52, which causes electrode shaft50 to rotate and extend tip electrode 36 from the distal end of lead 70.In this manner, tip electrode 36 may be screwed into the target tissuelocation. As such, coiled conductor 52 may have sufficient rigidity toassist in attaching tip electrode 36 to the target tissue location whilebeing flexible enough to navigate through body lumens, e.g., through oneor more veins. In other examples, tip electrode 36 may be extended via atranslational force instead of a rotational force. In other instances,electrode shaft 50 may be formed to receive a stylet to guide lead 70during implantation or to allow a user to extend and/or retract tipelectrode 36. In further instances, lead 70 may not include an electrodeshaft 50. Instead, conductor 52 may be directly connected to tipelectrode 36 and may or may not allow for mechanical control of tipelectrode 36.

Lead 70 includes an energy dissipating structure 88 that is electricallycoupled near the distal end of lead 70 to the electrical path from theproximal end of lead 70 to tip electrode 36. Energy dissipatingstructure 88 is electrically coupled to coiled conductor 52 throughoutat least a portion of transition section 91 to provide a secondelectrical path through energy dissipating structure 88 that is inparallel with the electrical path through tip electrode 36.

Energy dissipating structure 88 presents a high impedance at lowfrequencies, such as those frequencies used for pacing or otherstimulation therapies (e.g., ˜1 kHz for pacing signals). As such, only asmall amount of current is redirected away from tip electrode 36, e.g.,along the second electrical path to energy dissipating structure 88, atlow frequencies. In this manner, energy dissipating structure 88functions by essentially having electrical isolation at low pacingfrequencies allowing pacing to occur at the tip electrode surface.Energy dissipating structure 88 presents a low impedance at highfrequencies, such as those frequencies produced by MRI device 16(greater than 1.0 MHz), resulting in a significant amount of the inducedcurrent being redirected away from the first electrical path through tipelectrode 36 to the second electrical path through energy dissipatingstructure 88. Thus, energy dissipating structure 88 functions bycoupling a significant amount of the higher frequency energy through theenergy dissipating structure 88. In one example, an electrical lead withan energy dissipating structure 88 as described herein may result in atleast 50% of the energy induced by high frequency RF signals of an MRIdevice to be redirected away from tip electrode 36 while less than 10%of the energy associated with a pacing therapy is directed throughenergy dissipating structure 40.

In some instances, energy dissipating structure 88 has a surface areathat is significantly larger than a surface area of tip electrode 36.The surface area of energy dissipating structure 88 may, in one example,be between approximately 20-100 mm², which is at least approximately tentimes larger than the surface area of tip electrode 36. A large surfacearea ratio, defined by the ratio of the surface area of energydissipating structure 88 to the surface area of tip electrode 36 isdesired to dissipate the induced current over a larger area to reduceheating at any specific location.

Energy dissipating structure 88 may include a conductive material thatis at least partially covered by a layer of insulating material. In oneexample, the insulation material may cover at least the portion ofenergy dissipating structure 88 that is exposed to the bodily fluidand/or tissue of patient 12 such that the outer surface of theconductive material of energy dissipating structure 40 does not contacta body of the patient when implanted. In other instances, however,conductive material of energy dissipating structure 88 may be directlyexposed to bodily fluid and/or tissue, i.e., not include the layer ofinsulating material. The conductive material may be an electrically andthermally conductive material, such as titanium, titanium alloy,tantalum, tantalum alloy, platinum, platinum iridium, conductivepolymers, and/or other suitably conductive material or combination ofmaterials.

The insulating material may cover an outer surface of conductivematerial or at least a portion of the outer surface of conductivematerial. Insulating material may affect the impedance of energydissipating structure 88 and reduce the effect of energy dissipatingstructure 88 on the tip electrode to tissue interface impedances. As thethickness of insulating material increases, the capacitance associatedwith energy dissipating structure 88 decreases and the impedance ofenergy dissipating structure 88 increases. As a result the amount ofcurrent redirected to energy dissipating structure 88 is reduced, butthere is less interference with therapy delivered by IMD 22. As thethickness of insulating material 64 decreases, the capacitanceassociated with energy dissipating structure 88 increases and theimpedance of energy dissipating structure 88 decreases. As a result theamount of current (even at low frequencies) redirected to energydissipating structure 88 is increased, which may affect therapydelivered IMD 22.

For example, an energy dissipating structure 88 having a surface area ofapproximately 22 square millimeters (mm²) and an insulating materialhaving a dielectric constant of approximately 4.0, an insulatingmaterial thickness of approximately 68 micrometers provides an impedanceof approximately 10 Ohms and a capacitance of approximately 250 pF, athickness of approximately 34 micrometers provides an impedance ofapproximately 5 Ohms and a capacitance of approximately 500 pF, and athickness of approximately 17 micrometers provides an impedance ofapproximately 2.5 Ohms and a capacitance of approximately 1 nF. Thesevalues are only exemplary in nature. The electrical characteristics ofenergy dissipating structure 88 may take on different values dependingon the construction of the distal end of lead 70, e.g., based on thesurface area of tip electrode 36, the surface area of energy dissipatingstructure 88, the thickness of insulating material, the material fromwhich the various components are constructed, and the like.

The thickness of insulating material may be selected by a therapy systemdesigner to achieve a satisfactory tradeoff between capacitance andimpedance. Numerous techniques may be employed to introduce insulatingmaterial over the outside of energy dissipating structure 88 and/orpartially inside energy dissipating structure 88. Exemplary techniquesinclude chemical vapor deposition, dip layer, spraying, thermal reflow,or thermal extrusion or molding.

Insulating material may also cover at least a portion of an innersurface of conductive material. Insulating material on the inner surfacemay prevent conductive material of energy dissipating structure 88 frommaking direct contact with the conductive material of tip electrode 36,electrode shaft 50 and/or coiled conductor 52 at locations other thandesired. In some instances, the insulating material may even cover thesurface of the portion of conductive material contacting coiledconductor 52. In this case, the coupling between energy dissipatingstructure 40 and coiled conductor 52 is a non-conductive (e.g.,capacitive or thermal) coupling instead of a conductive coupling. Insome instances, energy dissipating structure 88 may include more thanone layer of insulating material, with each layer being made of the sameor different insulating material. Insulating material may includeparylene, metal oxides, polyimide, urethane, silicone,tetrafluroethylene (ETFE), polytetrafluroethylene (PTFE), polyetherether ketone (PEEK), oxides, or other suitable non-conductive materialor combination of materials.

It is desirable that the contact between energy dissipating structure 40and coiled conductor 52 is continuous, as intermittent metal-metalcontact of coiled conductor 52 and energy dissipating structure 40 maygenerate electrical noise. Moreover, with extendable\retractable leadsthis electrical connection/contact, the tip electrode 36 (which may be ahelix as illustrated in FIG. 3) and inner circuit (which may includecoiled conductor 52 and electrode shaft 50) may rotate while the energydissipating structure 40 remains fixed. It is thus desirable to have anelectrical connection/contact that reduces the effect on lead extensionperformance while maintaining constant contact and presents a lowresistance connection during MRI procedures. It may also be desirable tohave the connection/contact mitigate electrical noise that could begenerated via by intermittent metal-metal contact of inner circuit andenergy dissipating structure 40 or by this electrical connection. Noisegenerated by intermittent contact could present itself as cardiacsignals since the lead tip is moving at the same rate as the heart insome cardiac implementations. To help mitigate this noise potential theenergy dissipating structure 40 can be completely isolated with theexception of this electrical connection and/or this electricalconnection need to be of low enough resistance to drain off/ground themetal components resting potential such that noise is minimized by metalto metal contact.

Past solutions have been to make springs, spring clips, conductiveseals, or the like that will make these electrical connections. Theseoptions require that separate component(s) be added that makes contactwith electrode shaft 50. Some of these solutions may utilize componentsthat are constructed of a material that is harder than that of electrodeshaft 50 (which may be constructed of materials such as platinum/iridium(Pt/Ir)) so that the electrical connection component will not easilyplastically deform during assembly and use. The softer material ofelectrode shaft 50 may, in some instances, be subject to galling whenused in combination with harder spring materials. Additionally, thesmaller sizes and tolerances of the springs, spring clips, conductiveseals, or the like, make these components difficult and/or expensive tomanufacture.

In accordance with the techniques of this disclosure, lead 70 is formedto make electrical connection between coiled conductor 52 and the energydissipating structure 88 by way of an interference contact. Energydissipating structure 88 defines a lumen 90. Lumen 90 is offset relativeto lumen 76A. For example, lumen 90 and lumen 76A may lie in differentlongitudinal planes. In other words, a central axis of lumen 76A isoffset relative to a central axis of lumen 90. In the example of FIGS.7A and 7B, lumen 76A is offset toward an edge of lead body 74, whereaslumen 90 corresponds with a center of lead body 74, e.g., coiledconductor 52 transitions from an asymmetric lumen to center lumen.However, lumens 76A and 90 may both be offset relative toward the edgeof lead body 74, lumen 76A may correspond to a center of lead body 74and lumen 90 may be offset toward an edge of lead body 74, or the like.The configuration illustrated in FIGS. 7A and 7B is for illustrationpurposes only and should not be considered limiting of the design.

In the example of FIG. 7A, coiled conductor 52 transitions from lumen76A defined by the lead body 74 to a lumen 90 defined by energydissipating structure 88. This transition from lumen 76A of lead body 74to lumen 90 defined by energy dissipating structure 88 causes coiledconductor 52 to bend throughout at least a portion of transition section91. In this manner, conductor 52 is forced off center via a lumenposition change within lead body 74. Because coiled conductor 52 hasmany properties of a spring, when coiled conductor 52 is shifted out ofplane throughout transition section 91, the natural response of coiledconductor 52 is to realign along a relatively straight central axis. Assuch, coiled conductor 52 produces forces throughout at least a portionof transition section 91 in an attempt to realign the proximal anddistal ends of the transitioned section of coil 52. For example, coiledconductor 52 may exhibit forces at the proximal and distal ends oftransition section 91 to provide a relatively continuous interferencecontact near the proximal and distal ends of transition section 91.These forces may be utilized to provide a substantially continuouselectrical contact with energy dissipating structure 88.

In the example illustrated in FIG. 7A, a wire may be wound to form asecondary outer coil 94 that extends around the coiled conductor 52 tomake contact with coiled conductor 52 throughout at least a portion oftransition section 91. Secondary outer coil 94 may be mechanicallycoupled to energy dissipating structure 88, e.g., via crimping, welding,or the like. The end of secondary outer coil 94 opposite the connectionto energy dissipating structure 88 may not be connected mechanically toanything. The free floating end of secondary outer coil 94 proximate tothe lumen 76A may also have spring properties similar to those discussedabove with respect to coiled conductor 52 and thus provide forces to aidin the interference contact at portions of transition section 91. Inother instances, secondary coil 94 formed by the wire may providesufficient spring force to mechanically and electrically couple toenergy dissipating structure 88 without any crimping, welding, or thelike.

In some instances, secondary outer coil 94 may be formed to have aninner diameter that is approximately equal to or possibly slightlysmaller than the outer diameter of coiled conductor 52 when secondaryouter coil 94 is in its relaxed state. During assembly, secondary outercoil 94 may, in some instances, be pushed together, thus slightlyexpanding the diameter of the secondary coil 94. Coiled conductor 52 maybe strung through the pushed together the secondary outer coil 94 andthen the secondary outer coil 94 may be released to its relaxed state.When the secondary outer coil 94 is released to its relaxed statesecondary outer coil 94 may contact coiled conductor 52 throughout theentire portion or at least a large portion of the transition section 91,thus providing the interference contact.

Utilizing secondary outer coil 94 to provide the interference connectionwith energy dissipating structure 88 may enable movement and/or flexingthroughout the transition section 91 to minimize bending duringextension and retraction, and to allow a stylet to be moved in and outof this section more easily. The remainder of energy dissipatingstructure 88 may not be flexible.

In any case, the frictional force and contact between coiled conductor52 and secondary outer coil 94 provides an electrical connectionachieved by the friction between the coiled conductor 52 and secondaryouter coil 94. In this manner, the interference contact is accomplishedusing the inherent spring properties of coiled conductor 52 andsecondary outer coil 94.

In some instances, the coupling between energy dissipating structure 88and coiled conductor 52 throughout the transition section 91 may be viaa non-conductive coupling, e.g., capacitive coupling or thermalcoupling, to tip electrode 36 instead of an electrical (e.g., metal tometal) coupling. For example coiled conductor 52 and/or secondary outercoil 94 may be insulated throughout the transition portion, but stillallow high frequency RF energy to couple from coiled conductor 52through secondary outer coil 94 to energy dissipating structure 88.

The wire used to form secondary outer coil 94 may be a single filar ormulti-filar wire and may be round wire, flat wire, or other shaped wire.The wire used to form secondary outer coil 94 in the illustrated exampleis a dual-filar flat wire. In other examples, components other thansecondary outer coil 94 may provide the interference contact along thetransition segment 91, such as a wire mesh or other component.

FIG. 8 is a schematic diagram illustrating a view of a distal end ofanother example lead 93. The distal end of lead 93 substantiallyconforms to the distal end of lead 70 of FIG. 7, but energy dissipatingstructure 88 is an integral piece formed to provide the interferencecontact along at least a portion of transition section 91. In otherwords, the proximal end of energy dissipating structure 88 is formed,e.g., via bending, machining, or other technique, into a shape similarto transition segment 91 instead of utilizing a separate, secondaryouter coil 94 as described with respect to FIG. 7A. In this manner, theinterference contact is accomplished using the inherent springproperties of coiled conductor 52 creating contact with the portion ofenergy dissipating structure 88 extending along transition segment 91.

The portion of energy dissipating structure 88 formed to provide theinterference contact may, in some instance, be formed to allow formovement and/or flexing throughout the transition section 91 to minimizebending during extension and retraction, and to allow a stylet to bemoved in and out of this section more easily. For example, the portionof energy dissipating structure 88 formed to provide the interferencecontact may be formed relatively thin to provide the desired flexingwhile the remainder of energy dissipating portion 88 does not providemuch flex. In another example, the portion of energy dissipatingstructure 88 formed to provide the interference contact may include theone or more kerfs, grooves, or notches to allow that region of energydissipating structure 40 to bend or flex slightly allowing for moreintimate contact when the lead moves, as described above with respect toFIG. 4.

In some instances, the coupling between energy dissipating structure 88and coiled conductor 52 throughout the transition section 91 may be viaa non-conductive coupling, e.g., capacitive coupling or thermalcoupling, to tip electrode 36 instead of an electrical (e.g., metal tometal) coupling. For example coiled conductor 52 and/or the portion ofenergy dissipating structure 88 extending along transition segment 9lmay be insulated, but still allow high frequency RF energy to couplefrom coiled conductor 52 to energy dissipating structure 88.

FIG. 9 is a schematic diagram illustrating a view of a distal end ofanother example lead 95. The distal end of lead 95 substantiallyconforms to the distal end of lead 93 of FIG. 8, but energy dissipatingstructure 88 is composed of two separate portions that may provideeasier assembly and/or manufacturability. As illustrated in FIG. 9, afirst portion 92 of energy dissipating structure 88 is formed fromtransition section 91 toward the distal end of the lead and end nearwhere seal 56 of the assembled lead will be located. First portion 92 ofenergy dissipating structure may be formed via any of a number oftechniques including molding.

Second portion 92′ of energy dissipating structure 88 if formedseparately from first portion 92. Second portion 92′ may be formed withan indent arranged to receive a notch of insulation portion of the leadbody at location 97. In other instances, the insulation portion may beformed with an indent to receive a notch of second portion 92′. Ineither case, when second portion 92′ of energy dissipating structure 88is put into place, first portion 92 and second portion 92″ are in goodphysical and electrical contact to form energy dissipating shunt 88.First portion 92 and second portion 92′ may be constructed of the sameor different electrically and/or thermally conductive material.

Although FIGS. 7, 8, and 9 are described in the context of a lead thatinclude a conductive electrode shaft that is coupled at a proximal endto coiled conductor and coupled at a distal end to the tip electrode,these lead configuration may not include a conductive electrode shaft,but instead may have the coiled conductor directly connected to the tipelectrode.

FIG. 10 illustrates another example of a distal end of a lead 100, suchas one or both of leads 24 a or lead 24 b of FIG. 2. Lead 100 includes atip electrode 36 that is part of an electrical path from a proximal endof lead 100 that includes coiled conductor 104 and electrode shaft 50.Lead 100 is similar to lead 24 of FIG. 3 except energy dissipating shunt102 does not include protrusions designed to provide an interferencecontact with coiled conductor 104. Instead, the portion of coiledconductor 104 extending through the lumen formed by energy dissipatingstructure 102 is designed to provide an interference contact with energydissipating structure 102.

In the example illustrated in FIG. 10, coiled conductor 104 is formed tohave a larger outer diameter for a specific distance to create atinterference contact sections 106. In other words, coiled conductor 104includes sections 106 that have a larger outer diameter than theremaining portions of coiled conductor 104. These sections 106 have anouter diameter that is approximately equal to and possibly slightlylarger than the inner diameter of energy dissipating structure 102 suchthat an interference contact is made between these sections 106 ofcoiled conductor 104 and energy dissipating structure 102.

Sections 106 have inherent spring-like properties that are used togenerate/make the interference contact between the stationary energydissipating structure 102 and sections 106 of coiled conductor 104. Inparticular, the spring-like properties of sections 106 exert an outwardforce (e.g., away from a central axis of coiled conductor 104) thatprovides a constant contact between coiled conductor 104 and energydissipating structure 102. In instances in which lead 100 is an activefixation lead that is capable of extension and retraction, sections 106are designed to provide enough force to maintain continuous contact withenergy dissipating structure, but not impede the extension/retractioncapabilities of the lead during implantation. Sections 106 of coiledconductor 104 may, in some instances, be formed during winding. In otherinstances, sections 106 of coiled conductor 104 may be formed postwinding, e.g., during construction of the distal end of lead 100.

In the example illustrated in FIG. 10, each of the four filars of coiledconductor 104 have the larger outer diameter for at least one windingalong the longitudinal length of lead 100 to provide the interferencecontact. In other examples, fewer than all four filars of coiledconductor 104 may have the larger outer diameter. Coiled conductor 104illustrated in FIG. 10 has the larger outer diameter for a plurality ofturns 106 of coiled conductor 104 throughout the proximal portion ofenergy dissipating structure 102 thus providing the interferencecontact. In other examples, coiled conductor 104 may have the largerouter diameter for more or fewer turns of coiled conductor 104.

FIG. 11 illustrates another example of a distal end of a lead 110, suchas one or both of leads 24 a or lead 24 b of FIG. 2. Lead 110 includes atip electrode 36 that is part of an electrical path from a proximal endof lead 110 that includes coiled conductor 114 and electrode shaft 50.Lead 110 is substantially similar to lead 100 of FIG. 10 except theinterference contact between coiled conductor 114 and energy dissipatingstructure 102 is created by forming at least the portion of coiledconductor 114 extending through the lumen formed by energy dissipatingstructure 102 with a geometry to provide substantially continuouscontact with energy dissipating structure 102.

Coiled conductor 114 is constructed to have a pre-formed shape. Coiledconductor 114 may be pre-formed during winding or after winding, butprior to lead assembly of the distal end of lead 110 into a shape otherthan a typical straight conductor. For example, coiled conductor 114 maybe constructed into a J-shaped conductor and/or formed to include aloop. When the coiled conductor 114 having the pre-formed shape isplaced within the lumen defined by energy dissipating structure 102, thespring-like properties of coiled conductor 114 wanting to return to itspre-formed shape results in an interference contact with energydissipating structure 102. In the example illustrated in FIG. 11, theresulting shape of the portion of coiled conductor 14 through energydissipating structure 102 is an arc shape. In this manner, the coiledconductor 102 may be pre-formed with a geometry such that a controlledsections come in contact with the energy dissipating structure 102.Depending on the pre-formed shape of coiled conductor 114, the geometryof the portion of coiled conductor 114 extending within energydissipating structure 102 may have a shifting, sinusoidal, undulated orother geometry.

When assembled into lead 110, the geometry of the portion coiledconductor 114 extending within energy dissipating structure 102 isconfigured to provide a continuous contact with energy dissipatingstructure 102 at one or more locations, even during movement of lead110. In particular, coiled conductor 114 exerts a frictional force thatprovides a constant contact, but, at least in instances in which lead110 is an active fixation lead that is capable of extension andretraction, does not impede the extension/retraction capabilities of thelead during implantation.

FIG. 12 is illustrates another example of a distal end of a lead, suchas one or both of leads 24 a or lead 24 b of FIG. 2. This lead issubstantially similar to lead 110 of FIG. 11 except a preformed coil 122is placed within shunt 120 and a conventional, straight coiled conductor52 is extended through the pre-formed coil 122 to achieve theinterference contact.

It is understood that the present disclosure is not limited for use inpacemakers, cardioverters or defibrillators. Other uses of the leadsdescribed herein may include uses in patient monitoring devices, ordevices that integrate monitoring and stimulation features. In thosecases, the leads may include sensors disposed on distal ends of therespective lead for sensing patient conditions. The leads describedherein may be used with a neurological device such as a deep-brainstimulation device or a spinal cord stimulation device. In otherapplications, the leads described herein may provide muscularstimulation therapy, gastric system stimulation, nerve stimulation,lower colon stimulation, drug or beneficial agent dispensing, recordingor monitoring, gene therapy, or the like. In short, the leads describedherein may find useful applications in a wide variety medical devicesthat implement leads and circuitry coupled to the leads.

Various examples have been described. Most of the example leadconfigurations described include a conductive electrode shaft that iscoupled at a proximal end to coiled conductor and coupled at a distalend to the tip electrode. All of these example lead configurations,however, may not include a conductive electrode shaft, but instead mayhave the coiled conductor directly connected to the tip electrode.

Additionally, any of the lead configurations described herein mayinclude a kerf, groove or notch may be formed (e.g., via laser or othermechanism) on energy dissipating to allow that energy dissipatingstructure to bend or flex slightly allowing for more intimate contactwith the coiled conductor when the lead moves. The kerf, groove or notchmay be formed as described above with respect to FIG. 4.

These and other embodiments are within the scope of the followingclaims. Additionally, skilled artisans appreciate that other dimensionsmay be used for the mechanical and electrical elements described herein.It is also expected that the teachings herein, while described relativeto a bipolar lead, can also be applied to a unipolar lead or othermultipolar configurations as well as co-radial and multi-lumenconfigurations. These and other examples are within the scope of thefollowing claims.

The invention claimed is:
 1. A medical electrical lead comprising: alead body having a proximal end configured to couple to an implantablemedical device and a distal end; a conductive electrode shaft locatednear the distal end within the lead body; a coiled conductor extendingwithin the lead body from the proximal end and coupled to a first end ofthe conductive electrode shaft; an electrode located near the distal endof the lead body and coupled to an opposite end of the conductiveelectrode shaft as the coiled conductor; an energy dissipating structurelocated near the distal end of the lead body and formed from aconductive material that defines a lumen through which a portion of thecoiled conductor extends, wherein the portion of the coiled conductorextending through the lumen defined by the energy dissipating structureis formed to provide an interference contact with the energy dissipatingstructure; and a layer of insulating material covering at least an outersurface of the conductive material of the energy dissipating structuresuch that the outer surface of the conductive material of the energydissipating structure does not directly contact a body of the patientwhen implanted.
 2. The medical electrical lead of claim 1, wherein theportion of the coiled conductor extending through the lumen defined bythe energy dissipating structure is formed to have one or more sectionshaving windings of a first outer diameter and one or more sectionshaving windings of a second outer diameter, wherein the second outerdiameter is greater than the first outer diameter and the sectionshaving windings of the second outer diameter provide the interferencecontact with the energy dissipating structure.
 3. The medical electricallead of claim 2, wherein the lumen defined by the conductive material ofthe energy dissipating structure has an inner diameter and the secondouter diameter of the sections of the coiled conductor is approximatelyequal to the inner diameter of the lumen defined by the conductivematerial of the energy dissipating structure.
 4. The medical electricallead of claim 2, wherein the lumen defined by the conductive material ofthe energy dissipating structure has an inner diameter and the secondouter diameter of the sections of the coiled conductor is larger thanthe inner diameter of the lumen defined by the conductive material ofthe energy dissipating structure.
 5. The medical electrical lead ofclaim 1, wherein the coiled conductor has a pre-formed geometry suchthat the portion of the coiled conductor extending through the lumendefined by the energy dissipating structure provides the interferencecontact with the energy dissipating structure.
 6. The medical electricallead of claim 5, wherein the portion of the coiled conductor extendingthrough the lumen defined by the energy dissipating structure is shapedinto one of an arc and an undulated pattern.
 7. The medical electricallead of claim 6, wherein the interference contact between the energydissipating structure and the portion of the coiled conductor extendingthrough the lumen defined by the energy dissipating structure issubstantially continuous during movement of the lead.
 8. The medicalelectrical lead of claim 5, the coiled conductor being pre-formed toinclude one of a J-shape or a loop toward a distal portion of the coiledconductor such that when the distal portion of the coiled conductor isplaced within the lumen defined by the energy dissipating structure,spring-like properties of the coiled conductor wanting to return to itspre-formed shape results in the interference contact with the energydissipating structure.
 9. The medical electrical lead of claim 1,wherein a large portion of current induced on the coiled conductor byhigh frequency signals is redirected to the energy dissipating structurewhile a small portion of the current produced on the coiled conductor bylow frequency therapy signals is redirected to the energy dissipatingstructure.
 10. The medical electrical lead of claim 1, wherein thecoupling of the conductive electrode shaft, the coiled conductor, andthe electrode provides a mechanical relationship that allows formechanical control of the electrode to extend the electrode from thedistal end of the lead body.
 11. The medical electrical lead of claim 1,wherein the coupling of the conductive electrode shaft, the coiledconductor, and the electrode provides a mechanical relationship thatallows for mechanical control of the electrode to extend the electrodefrom the distal end of the lead body while the energy dissipatingstructure remains stationary.
 12. An implantable medical systemcomprising: an implantable medical device; and an implantable medicalelectrical lead, wherein the implantable medical electrical leadincludes: a lead body having a proximal end configured to couple to theimplantable medical device and a distal end; a conductive electrodeshaft located near the distal end within the lead body; a coiledconductor extending within the lead body from the proximal end andcoupled to a first end of the conductive electrode shaft; an electrodelocated near the distal end of the lead body and coupled to an oppositeend of the conductive electrode shaft as the coiled conductor; an energydissipating structure located near the distal end of the lead body andformed from a conductive material that defines a lumen through which aportion of the coiled conductor extends, wherein the portion of thecoiled conductor extending through the lumen defined by the energydissipating structure is configured to provide an interference contactwith the energy dissipating structure that is substantially continuous;and a layer of insulating material covering at least an outer surface ofthe conductive material of the energy dissipating structure such thatthe outer surface of the conductive material of the energy dissipatingstructure does not directly contact a body of the patient whenimplanted.
 13. The medical electrical system of claim 12, wherein theportion of the coiled conductor extending through the lumen defined bythe energy dissipating structure is formed to have one or more sectionshaving windings of a first outer diameter and one or more sectionshaving windings of a second outer diameter, wherein the second outerdiameter is greater than the first outer diameter and is at leastapproximately equal to an inner diameter of the lumen defined by theconductive material of the energy dissipating structure such that thesections having windings of the second outer diameter provide theinterference contact with the energy dissipating structure.
 14. Themedical electrical system of claim 12, wherein the coiled conductor hasa pre-formed geometry such that the portion of the coiled conductorextending through the lumen defined by the energy dissipating structureprovides the interference contact with the energy dissipating structure.15. The medical electrical system of claim 14, wherein the portion ofthe coiled conductor extending through the lumen defined by the energydissipating structure is shaped into one of an arc and an undulatedpattern.
 16. The medical electrical system of claim 15, the coiledconductor being pre-formed to include one of a J-shape or a loop towarda distal portion of the coiled conductor such that when the distalportion of the coiled conductor is placed within the lumen defined bythe energy dissipating structure, spring-like properties of the coiledconductor wanting to return to its pre-formed shape results in theinterference contact with the energy dissipating structure having one ofthe arc or the undulated pattern.
 17. The medical electrical system ofclaim 12, wherein the coupling of the conductive electrode shaft, thecoiled conductor, and the electrode provides a mechanical relationshipthat allows for mechanical control of the electrode to extend theelectrode from the distal end of the lead body while the energydissipating structure remains stationary.
 18. A medical electrical leadcomprising: a lead body having a proximal end configured to couple to animplantable medical device and a distal end; an electrode located nearthe distal end of the lead body; a coiled conductor extending within thelead body from the proximal end and coupled to the electrode; an energydissipating structure located near the distal end of the lead body andformed from a conductive material that defines a lumen through which aportion of the coiled conductor extends, wherein the portion of thecoiled conductor extending through the lumen defined by the energydissipating structure is formed to provide an interference contact withthe energy dissipating structure that is substantially continuous; and alayer of insulating material covering at least an outer surface of theconductive material of the energy dissipating structure such that theouter surface of the conductive material of the energy dissipatingstructure does not directly contact a body of the patient whenimplanted.
 19. The medical electrical lead of claim 18, wherein theportion of the coiled conductor extending through the lumen defined bythe energy dissipating structure is formed to have one or more sectionshaving windings of a first outer diameter and one or more sectionshaving windings of a second outer diameter, wherein the second outerdiameter is greater than the first outer diameter and is at leastapproximately equal to an inner diameter of the lumen defined by theconductive material of the energy dissipating structure such that thesections having windings of the second outer diameter provide theinterference contact with the energy dissipating structure.
 20. Themedical electrical lead of claim 18, wherein the coiled conductor has apre-formed geometry such that the portion of the coiled conductorextending through the lumen defined by the energy dissipating structureprovides the interference contact with the energy dissipating structure.21. The medical electrical lead of claim 20, wherein the portion of thecoiled conductor extending through the lumen defined by the energydissipating structure is shaped into one of an arc and an undulatedpattern.
 22. The medical electrical lead of claim 21, the coiledconductor being pre-formed to include one of a J-shape or a loop towarda distal portion of the coiled conductor such that when the distalportion of the coiled conductor is placed within the lumen defined bythe energy dissipating structure, spring-like properties of the coiledconductor wanting to return to its pre-formed shape results in theinterference contact with the energy dissipating structure having one ofthe arc or the undulated pattern.